1. Field of the Invention
The present invention relates to an organic thin film transistor, a production method thereof, and an electronic device. More particularly, the invention relates to a bottom-contact type organic thin film transistor formed of a source electrode and drain electrode with an organic semiconductor layer formed thereon, a production method of the organic thin film transistor, and an electronic device provided with the organic thin film transistor.
2. Description of the Related Art
Thin film transistors using an organic semiconductor layer as an active layer, the so-called organic thin film transistors, have been attracting much attention in recent years. Since the organic semiconductor layer as the active layer in the organic thin film transistor can be formed by a film coating method at relatively low temperatures, this is advantageous for reducing production costs, also enables its formation on a flexible, low heat-resistant substrate made of plastic and so forth. In addition, not only for the active layer, but also for a gate insulating film, source/drain electrode, and gate electrode, the patterning formation becomes feasible by employing the printing method using coating agent materials, thereby allowing a further reduction of production costs to be feasible, as well as allowing a large increase in the substrate size.
In order to improve transistor characteristics in the organic thin film transistor mentioned above, it is important to employ a source/drain electrode which can achieve a good ohmic contact with the organic semiconductor layer. As the materials suitable for forming such source/drain electrode among inorganic materials, gold (Au), platinum (Pt), and also palladium (Pd) have been utilized, for example. These materials are known to yield satisfactory ohmic contact with p-type organic semiconductors. In addition, as to organic materials there reported is the use of poly-ethylenedioxythiophene and polystyrene sulphonic acid in combination, doped polyaniline, carbon nanotube, and so forth.
Moreover, the methods of forming the source/drain electrode aimed at extended device life have been also proposed. In this case, a base layer formed of titanium nitride (TiNx) or conductive paste is disposed by a patterning method, the thus formed pattern is subsequently subjected to the formation of a nickel (Ni) layer by electroless plating method, and further the surface of the Ni layer is displaced by Au employing displacement plating techniques. As a result, the source/drain electrode is formed having the structure with the base layer formed of titanium nitride (TiNx) or conductive paste which is covered with Au layer through Ni layer (see, for example, Japanese Unexamined Patent Application Publication No. 2001-203364).